No convincing explanation exists for the aggressive growth of Kaposi's sarcoma (KS) in the estimated 8 million people worldwide afflicted with both this disease and human immunodeficiency virus type 1 (HIV-1). Human herpesvirus 8 (HHV-8) is required for the development of KS but is insufficient to cause it unless a second factor, such as HIV-1, is present. The HIV-1 transactivator of transcription (Tat) protein is implicated in KS because it stimulates the invasive and proliferative properties of KS cells and endothelial cells (ECs) in cultures and in tat transgenic mice. In preliminary studies, we found that Tat activates phosphatidylinositol 3'-kinase (PI3K) and Akt, the latter is a key regulator in tumorigenesis and cell survival. We found that immobilized Tat and physiologic levels of Tat in solution promoted the survival of KS SLK cells. It is not known how Tat promotes cell survival or to what extent this effect promotes growth of KS. We hypothesize that HIV-1 Tat activates Akt and promotes cell survival. Our preliminary studies with Tat and our exclusive faf transgenic mice lines will enable us to evaluate Tat's role in PI3K-Akt activation and cell survival. Specific Aim 1. Determine to what extent Tat activates Akt In vitro, and identify the signaling pathway Tat uses to promote cell survival. We will characterize Tat-related Akt phosphorylation and Akt kirtase activity in HHV-8 infected dermal microvasculature endothelial (HHV8-OMVE) cells. We will map the active moiety in Tat by using peptides, truncated Tat mutants, and antibodies. We will target the PI3K-Akt pathway with drugs (LY294002 and Perifosine) and PI3K-AM dominant-negative mutants to determine the role of this pathway in Tat-related cell survival. Specific Aim 2. Determine to what extent Tat activates Akt In vivo and promotes tumor growth by analyzing Tatexpressing cells In nude mice and tat transgenic mice. Tat of different sizes will be expressed and mapped on Tat domains critical to Akt phosphorylation. We will also test designed PISK-Akt inhibitors (LY294002 and Perifosine) and candidate anticancer agents for their role in blocking this pathway and reversing tumor growth. Successful completion of these studies will help identify a novel property of Tat that stimulates a survival mechanism anticipated to play a major role in KS and HHV8-DMVE cells. This research plan will establish the potential of drugs designed to interrupt this pathway implicated in KS and perhaps in other cancers associated with HIV-1 infection.